Eddy current disk mechanism



y 1952 w. BUTLER EDDY CURRENT DISK MECHANISM Filed April 5, 1946 M M. 73 s r I w u. n m e m 2 r n e 0 mg a mm k. t m 9 W b W Patented May 13,1952 UNITED EDDY CURRENT DISK MECHANISM William Lawrence Butler,Schenectady, N. Y., assignor to General Electric Company, a corporationof New York Application April 5, 1946, Serial No. 659,717

1 Claim. 1

My invention relates to eddy current disc mechanism, more particularlyto direction responsive eddy current disc clutch mechanism, and has forits object a simple and reliable direction responsive clutch for useespecially in the operation of electric switches.

The clutch disclosed herein i particularly useful with the electricswitch mechanism disclosed in my copending application Serial No.216,216, which is a division of the present application and is assignedto the assignee of the present application, however, this clutch is notlimited in its adaptability to such a switch mechanism.

In carrying out my invention in one form I provide a shaft havingrigidly mounted thereon an eddy current disc made of electricallyconducting material. Also mounted rotatably on the shaft on oppositesides of the disc are two supporting disc members on which are mountedaround their peripheries a plurality of small permanent magnets havingtheir pole faces adjacent the disc. Also, the magnets are arranged inaxially opposed pairs with unlike poles axially opposite each other.Rotation of the shaft and disc between the poles of the magnets produceseddy currents in the disc whereby a magnet torque is applied to the discsupporting structure for the magnets. The supporting structure ismounted for limited angular movement in each direction and is providedwith an operating arm which may be arranged to actuate a single pole,double throw switch.

For a more complete understanding of my invention reference should behad to the accompanying drawing, Fig. 1 of which is a side elevationview with the enclosing casing in section showing a switch mechanismembodying my invention; Fig. 2 is an end view of Fig. 1 with the coverremoved; Fig. 3 isa sectional view taken along line 33 of Fig. 1 lookingin the direction of the arrows, Fig. 4 is a sectional view taken alongthe line 4-4 of Fig. 1 looking in the direction'of the arrows, whileFig. 5 is a sectional view of the eddy current disc.

Referring to the drawing, in one form of my invention I provide a metalenclosure r casing comprising a cylindrical portion I to the right handend of which is integrally joined a rectangular portion 2. Mounted inthe cylindrical portion I is a shaft 3 having its lefthand end as seenin Fig. 1 projecting from the casing for connection through a suitablecoupling to a source of rotational energy such as the shaft of anelectric motor to be controlled. The shaft 3 is mounted in a ballbearing 4 mounted in the lefthand end wall of the enclosure portion I,and a ball bearing which is mounted on a supporting 2 plate 6 secured bysuitable screws 1 to the lefthand wall of the enclosure portion 2.Preferably, as shown, the shaft is supported by the bearings 4 and 5with its axis of rotation coaxial with the center line of the enclosureI.

The shaft 3 drive an eddy current disc 8, which is rigidly secured tothe shaft, between axially disposed permanent magnets carried by asupporting structure 9 rotatably mounted on the shaft. As shown, thissupporting structure for the permanent magnets consists of supportingdiscs I0 and II mounted on central bearings I2 and I3 secured to theshaft 3. At their peripheries the two discs I0 and II are rigidlyconnected together by axially extending straps I4, I5, and I6 whichextend across the periphery of the disc 8 in spaced relation therewith.It will be understood that the two discs I0 and II and the connectingmembers I4, I5 and I6 are made of a suitable non-magnetic and preferablylight material such as aluminum.

As shown in Fig. 3, five small bipolar permanent magnets I! to 2 I,inclusive, are mounted on the disc I0 on the side adjacent the eddycurrent disc 8 and with the two poles of each magnet in closely spacedrelation with the eddy current disc. The magnets are convenientlysecured in place each by a screw 22 extending centrally through it andinto a tapped hole in the disc I0. Preferably as shown, the magnets areequally spaced apart around the periphery of the disc II] with unlikepoles of adjacent magnets adjacent each other. An identical set of fivemagnets, only three of which are shown and indicated by referencenumerals 23, 24 and 25, are mounted on .the disc II in the same equallyspaced relation with each other and with each magnet directly oppositeaxially a magnet on the disc I0. As shown, the magnet 24 is directlyopposite the magnet I9 thereby to form a pair of axially oppositelydisposed magnets. Moreover, the magnets of each oppositely disposed pairare arranged with their north poles, axially opposite their south poles,as indicated by the letters N and S on the magnets I9 and 24. Thisrelative pole positional arrangement of the magnets provides for themaximum generation of eddy currents and the maximum torque.

As the disk 8 is rotated in the magnet field produced by the permanentmagnets eddy currents are set up in the disc whereby a torque isproduced tending to rotate the magnet supporting structure 9 in the samedirection as the disc 8 is being driven. This rotation of the structure9 is limited to a small angle by means of an operating member 26 made ofelectrically insulating material having one end secured to the disc Hand extending parallel with the shaft 3 through a rotation limitingaperture 21 in the supporting plate 6. At its opposite end the member 26is provided with a slot 28 through which extends the end of a flexibleswitch arm 29 the other end of which is secured to a bracket 30 mountedon a supporting block 3| made of a molded electrically insulatingmaterial. A switch contact 32 on the movable end of the arm 29cooperates with stationary contacts 33 and 34 on opposite sides of theswitch arm so as to engage one or the other of the stationary contactsin dependence upon the direction of the rotation of the magnetsupporting structure 9. It will be observed that the switch arm and twostationary contacts form a single pole double throw switch.

The magnet supporting structure 9 and the switch arm are biased to anintermediate position with the switch arm midway between the twostationary contacts by means of two helical springs 35 and 36, as shownin Fig. 4, on the side of said support 3| opposite the switch arm. Thesprings are secured each at one end respectively to spring tensionadjusting members 31 and 38 which are in turn secured by screws 39 and4D to the insulating support 3|. The opposite ends of the springs aresecured respectively to arms 4| and 42 mounted on pivots 43 and 44secured to the molded support 3|. As shown in Fig. 4, the arms 4| and 42are biased by the springs against a projection 45 extending between themand formed integrally with the support 3|. Extending between therighthand ends of these arms as seen in Fig. 4 is the operating member26 whereby the springs bias the operating member, the magnet supportingstructure and the switch arm in their intermediate positions shown. Theright ends of the arms 4| and 42, as seen in Fig. 4, move between thewalls Ma and 42a of the recess in the support 3| into which the endsextend.

In order that the lefthand ends of the arms as seen in Fig. 4 mayoverlap, the arm 42 is somewhat lower than the other arm so that itsleft end is free to move under the lefthand end of the other arm. Aprotuberance 45 is provided on the lower side of the arm 4| which rubson the arm 42 thereby providing a minimum of friction between them. Asimilar protuberance, not shown, is provided on the upper side of thearm 42 which engages the lower side of the arm 4|.

For the purpose of latching the movable parts in their intermediateposition shown when the driving motor is deenergized, a pivoted latch 41is provided having its lower end as seen in Fig. 4 bent toward the rightand extending between the arms 4| and 42 whereby pivotal movement of thearms is prevented. When the motor is energized the latch 47 is movedabout its pivot 48 in a clockwise direction by a magnet 49 mounted on abracket 50 which in turn is mounted on the support 3|, the pivot 48being mounted on the bracket. The coil of the magnet has its terminalsconnected to connectors 52 and 53 on the front side of the support 3| asseen in Fig. 2.

To facilitate adjustment of the force applied by the spring 35, a cam 54is provided having an aperture through which extends the screw 39. Thiscam engages a projection 55 on the member 31 which has a slot (notshown) for the screw 39. After loosening the screw 39, the member 31 maybe moved about a pivot 56 at its lower end to adjust the tension of thespring 35, after which the cam is turned to a position to contact themember 31 and the screw 39 is then tightened. A similar adjustment isprovided for the member 38 and spring 36. The pivot 56 is convenientlyformed by extruding a hole in the lower end of the member 31 whereby acircular flange (not shown) is provided on its lower side, which flangeseats in an aperture in the support 3|. It will be understood thatadjustment of the springs adjusts the device for opening of the switchat a predetermined low speed of the shaft 3 whereby the driving motor isdeenergized and coasts to a standstill.

The support 3| is secured to the plate 6 by means of screws 51 and 58and by removing these screws the support with all of the parts mountedon it may be removed. In a similar manner the plate 6 may then beremoved by removing the screws 1 after which the shaft 3 and the supportstructure 9 can be removed. A cover 59 is provided for the enclosureportion 2. The device may be mounted on a suitable support by means ofscrews or bolts passing through the apertures 60 .to 63 inclusive.

Electric conductors for connectin the coil 5|, the two stationarycontacts, and the contact arm 29 in their control circuits are led inthrough an aperture 84 in the rectangular enclosure portion 2. Theelectric connections for connecting the switch for the control of athree-phase motor may be as shown in Fig. 3 of U. S. Patent No.2,141,278 issued to Joseph W. Owens on December 27, 1938 for switchmechanism. In addition, the terminals of the coil 5| are connecteddirectly across two terminals of the motor so that the coil is energizedand the latch 41 moved to release the arms 4| and 42 only when the motoris energized. The latch is provided for the purpose of preventing theclosure of the switch inad vertently when the shaft of the driving motoris turned manually, which is sometimes done for the purpose of adjustingthe apparatus driven by the motor while the motor is deenergized. Itwill be understood that closure of the switch by movement of the contactarm 29 into engagement with either one of the stationary contactseffects the closure of one or the other of the starting contactors andenergization of the motor.

The permanent magnets mounted on the supporting structure 5 preferablyare made of a material having a high coercive force and high resistanceto change in magnetic properties. One such material is an alloy of 12percent aluminum, 25 percent nickel and 5 percent copper, the balancebeing mainly iron, such as described and claimed in Patent 1,947,274,issued on February 13, 1934, to William E. Ruder and Patent 2,027,997,issued on January 1, 1936, to Tokushichi Mishima.

As shown in Fig. 5, for the purpose of increasing the torque I providetubular flanges 65 and 66 on opposite sides of the eddy current disc 8and concentric with the axis of rotation of the disc. These flanges areeach inside of its series of magnets, two of which, such as I8 and 23,are indicated in dotted lines. The flanges serve the purpose ofproviding a conducting path for eddy curcents of increased crosssection, and therefore, decreased resistance, whereby the flow of eddycurrents and hence torque is increased. In a typical device I found thatthese flanges on the disc increased the torque applied to the magnetsupporting structure from ten to twenty percent.

A similar pair of flanges on the outer periphery of the disc outside ofthe magnets would serve to give a still greater increase in torque but,for manufacturing reasons, I prefer not to use such flanges on theperiphery of the disc. Instead, I

mount the permanent magnets in such positions that they are inside theperiphery of the disc, as shown clearly in Fig. 3, i. e., they arespaced from the periphery. The metal of the disc outside of the magnetsserves to some extent to provide a path of decreased resistance for eddycurrents whereby the torque is increased.

It will be noted that the disc 8 is of substantial thickness which alsois for the purpose of providing a low resistance path for the fiow ofeddy currents. In a typical device the disc was onequarter inch thick,while the distance between the two poles of each magnet, i. e., thewidth of the air gap between the two poles was also onequarter inch. Thedisc is preferably made of good copper having a conductivity ninety-fivepercent of the conductivity of pure silver. It will be understood thatthe thickness of the disc for maximum torque is a compromise between theair gaps between the poles of each magnet and between the poles ofoppositely disposed magnets. If the thickness of the disc is decreased,oppositely disposed magnets will be closer together and, therefore, givemore magnetic flux through the disc but, on the other hand, thedecreased thickness of the disc gives increased resistance to the flowof eddy current. On the other hand, if the disc, and therefore the airgap between oppositely disposed magnets, is too great, the magnetic fluxwill tend to pass between the two poles of each magnet without passingthrough the disc, with resulting decrease in torque.

It will be noted that, because of the spacing between the magnets andthe disc, the distance between the poles of oppositely disposed magnetsis somewhat greater than the width of the slot between the two poles ofeach magnet, although the distance between oppositely disposed poles isvery considerably less than the distance from center to center of thepole faces of each magnet.

The efiicient distribution of the magnetic field for the generation ofeddy current is further increased by spacing the magnets apart, as seenin Fig. 3, at such distances that the effective distance between theadjacent poles of separate magnets is substantially the same a thedistance between the two poles of a single magnet.

As shown in Fig. 5, I have provided a series of holes 61 in the web ofthe disc joining the flanges 65 and 66 with the hub 68. Preferably, sixequally spaced holes are provided in this web. These holes serve thepurpose of reducing the cross section of the disc thereby to reduce theloss by conduction of heat from the outer portion of the disc in whicheddy currents are generated, whereby that portion is heated more quicklyto a stable operating temperature providing the ultimate operatingtorque for which the switching device is calibrated. This rapid heatingof the dis-c is desirable to prevent non-uniform operation in the eventthat the motor is plugged before the disc is heated to its calibratedtemperature. In such case the contacts would open later because of theincreased torque at the lower disc temperature with undesirable controlof the motor. It will be understood that the copper disc has a positivetemperature coefficient of resistance with higher resistance anddecreased torque at the higher temperatures.

I have also found that increased torque is provided by arranging eachmagnet as seen in Fig. 3 with the centers of both of its poles lying ona circle whose center is the axis of rotation of the disc, 1. e.equidistant from the shaft. This arrangement gives the greatest possibletorque 6 about the axis of rotation. At high speeds the torque islimited by the leakage of flux directly between the two poles of eachmagnet.

While I have shown a particular embodiment of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made and I therefore contemplate by theappended claim to cover any such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

An eddy current disc mechanism comprising a shaft mounted for continuousrotation, a flatly disposed eddy current disc secured to said shaft forrotation therewith, a movably mounted supporting member arranged forlimited rotation about the rotational aXis of said shaft, a plurality ofbi-polar permanent magnets mounted on said supporting member in equallyspaced relation with each other on each side of said disc, said magnetsbeing constructed each with its poles spaced apart a distancesubstantially equal to the thickness of said disc, the centers of bothpoles of the magnets on one side of said eddy current disc coincidingapproximately with a circle having its center on said axis and thecenters of both poles of the magnets on the other side of said eddycurrent disc coinciding approximately with a circle of the same diameteras said first circle and also having its center on said axis, themagnets on each side of said disc having unlike poles adjacent eachother and the distance between adjacent poles of separate magnets beingsubstantially the same as the distance between the two poles of a singlemagnet, and the magnets adjacent opposite surfaces of said disc beingarranged with unlike poles directly opposite each other on oppositesides of said disc in a direction parallel with said axis.

WILLIAM LAWRENCE BUTLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 446,488 Waring Feb. 17, 1891568,046 Spratt Sept. 22, 1896 653,424 Lunt July 10, 1900 847,597 Onsumet al Mar. 19, 1907 908,707 Steckel Jan. 5, 1909 912,504 Steckel et a1Feb. 16, 1909 1,058,885 Meyer Apr. 15, 1913 1,222,720 Bijur Apr. 17,1917 1,756,671 Alden Apr. 29, 1930 1,960,915 Morse May 29, 19342,125,055 Taliaferro July 26, 1938 2,141,278 Owens Dec. 27, 19382,206,696 Hall July 2, 1940 2,209,368 Whittaker July 30, 1940 2,263,264Duwe Nov. 18, 1941 2,293,748 Johnson Aug. 25, 1942 2,298,521 UehlingOct. 13, 1942 2,300,773 Cornwell Nov. 3, 1942 2,361,239 Ransom Oct. 24,1944 2,443,623 Koenig, Jr June 22, 1948 2,465,932 Romine Mar. 29, 19492,470,928 Halter May 24, 1949 FOREIGN PATENTS Number Country Date 28,845Great Britain of 1910 107,144 Great Britain Apr. 23, 1939

